Observation of Atomic Antihydrogen

We report the background-free observation of atomic antihydrogen, produced by interactions of an antiproton beam with a hydrogen gas jet target in the Fermilab Antiproton Accumulator. We measure the cross section of the reaction $\overline{p}p\to \overline{H}{e}^{-}p$ for $\overline{p}$ beam momenta between 5203 and 6232 MeV/ $c$ to be $1.12\pm 0.14\pm 0.09$ pb.